Radio telegraph receiving system



Sept. 27, 1938. P. D. LOWELL 2,131,109

RADIO TELEGRAPH RECEIVING SYSTEM I Filed July 25, 1953 Patented Sept.27, 1938 UNITED STATES RADIO TELEGRAPH RECEIVING SYSTEM Percival D.Lowell, Chevy Chase, Md., assignor to Radio Corporation of America, NewYork, N. Y., a corporation of Delaware Application July 25, 1933, SerialNo. 682,132

9 Claims.

My invention relates broadly to radio receiving apparatus and moreparticularly to apparatus for the reception of continuous wave radiotelegraph code signals.

One of the objects of my invention is to provide a circuit arrangementfor a continuous wave radio telegraph receiving system having means forstabilizing the tone frequency of the received signals.

Another object of my invention is to provide an improved superheterodynetype of radio receiving circuit for the reception of continuouswavetelegraph signals having means for stabilizing the tone frequency of thereproduced telegraphic signals.

Still another object of my invention is to provide a circuit arrangementfor superheterodyne type of radio receiving systems wherein the highfrequency oscillator which coacts with the first detector iscontinuously modulated at a constant frequency adapted to be selectivelyimpressed upon the audio frequency signal output circuit in accordancewith the received telegraphic signals.

Still another object of my invention is to provide a continuous wavesuperheterodyne type of radio telegraph receiving system including ahigh frequency oscillator arranged to coact with a first detector incombination with a source of audio frequency modulating energy which isadapted to be transferred through the intermediate frequency amplifier,second detector and audio frequency amplifier of the superheterodynereceiver in accordance with the telegraphic signals which are receivedfor thereby determining the character of the audio frequency signalingenergy which is delivered to the audio frequency signal output circuit.

7 A further object of my invention is to provide a circuit arrangementfor the selective reception of radio telegraph signals through asuperheterodyne receiving circuit with minimum interference from staticor undesired signals in which a source of audio frequency signalingenergy at the receiver is rendered efiective upon a preselector circuitof an audio frequency amplification system which static high frequencyoscillator which coacts with the first detector is modulated at apredetermined audio frequency rate to which the audio frequencyamplification system is selectively tuned whereby theincomingtelegraphic signals effect the transfer, through theintermediate frequencyamplifier and second detector to the audiofrequency amplification system, of that frequency to which the audiofrequency amplification system is selectively adjusted. I I

Other and further objects of my invention reside in the selectivecontinuous wave. radio telegraph signal receiving system as set forthmore fully in the specification hereinafterfollowing by reference .tothe accompanying drawing which Vention. V

.,In. thelcircuits now commonly used in radio telegraphy it is customaryto employ either an oscillating detector or a separate oscillator forthe ,purpose. of generatingoscillati'ons to beat with the incomingsignal waves, thereby rendering the:

incoming code signals audible to, the ear or useful in operatingarecorder'or printer; It is the purpose of my invention to provide amore stable,

simpler and-more easily. adjusted method of rendering the continuouswave signals audible than that obtainable in'the usual beat frequency.

'the incoming signal frequency to a frequency of a different value. Ihavefound that if the oscillator inasuperheterodyne receiving system becontinuously modulated at. aconstantaudio frequency, this audiofrequency will not pass through the intermediate frequency amplifier,second detector and 'audiofrequency amplifier unless a continuous. waveincoming signal isalso present. In otherwords, an incoming continuouswave signal When'it reaches the oscillator, besides being converted to adifferent frequency, also becomes modulated at the audio frequency. Theconverted andmodulated signal will then pass through the intermediatefrequency amplifier, second detector andaudio frequency amplifier andthe dots and dashes will be reproduced at thefrequency of the audiomodulation. The system of my invention is rendered especially selectiveby reason of the. peaked characteristic of the audio frequency amplifierat a certain frequency. I may also employ an audio frequency amplifierhaving a sharp band passcharacteristic for the purpose of eliminatinginterference or reducing the response of the re-,

ceiver to static disturbances. The audio frequen cy responsecharacteristic of the audio frequency amplifier system is selectedtocorrespond to the modulation and frequency ofth-e highfrequencyoscillator, thereby rejecting -undesired signal fre i superheterodynereceiver circuit comprising the antenna circuit l, the radio frequencyamplifier 2, the first detector 3, the oscillator 4, the intermediatefrequency amplifier 5, second detector 6, audio frequency amplifier "I,and audio frequency output circuit 8 which connects to a signalindicating device, recorder or printing mechanism. The oscillator 4 ismodulated by the source of audio voltage I which is introduced into theoscillator circuit through the coupling transformer 9. The couplingtransformer 9 includes a primary winding H connected with the source ofaudio voltage I 0 and a secondary winding l2 connected in series withthe input circuit of the oscillator between the biasing resistor l4 andthe lower terminal of the tuned circuit 15. The oscillator includes thecoupling coil IS in the output circuit thereof inductively related tothe inductance of the tuned circuit [5 in the input circuit of theoscillator. The high frequency oscillations generated by oscillator 4-are impressed upon the circuit of the first detector 3 by theelectro-magnetic coupling between oscillator coils l5, l6 and the tunedgrid circuit of the detector 3. The source. of potential [8 suppliesplate excitation for all of the electron tubes. I have illustrated theindirectly heated type of electron tube employed in the oscillator andthroughout the several stages of the receiver. The audio frequencyamplificationsystem which has been represented for purposes ofexplaining my invention, has a single amplifier stage, preceded by apreselector circuit which I have designated at I9. The preselectorcircuit includes the secondary Winding audio frequency transformer 20with a condenser 2| connected in shunt I thereto and adjusted. to theaudio frequency produced by the source of audio voltage Ill. Inasmuchasthe tuned circuit 19 is selectively responsive to the frequency of themodulator Hl, interfering. frequencies and static effects produce aminimum effect upon audio frequency amplification system 1. The tunedcircuit I9 is matched to the frequency of the modulator Ill. Thefrequency of the modulator ID will not pass through the intermediateamplifier 5 or the second detector E to the transformer 20 andpreselector circuit I9 unless a continuous wave incoming signal is alsopresent. When a continuous wave incoming signal reaches the oscillator,the beat or intermediate frequency thereby produced isv impressed uponthe intermediate frequency amplifier 5 and at the same time themodulation to say, thehigh frequency path from the end of tuned circuitl5 to the'cathode of tube 4 is closed through condenser 22 whileallowing audio frequency oscillations to be impressed from source I0upon the input circuit of the'oscillator '4.

I have found the continuous wave: receiving 75.:system of my inventionhighly practical in its:-

operation. I have used the circuit in the operation of automaticprinters by radio with highly successful results over substantialdistances. While I have described my invention in one of its preferredembodiments, I desire that it be understood that modifications may bemade and that no limitations upon my invention are intended other thanare imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. A continuous wave radio telegraph receiving system comprising asuperheterodyne receiving circuit including a first detector, a highfrequency oscillator connected therewith, an intermediate frequencyamplifier connected with said first detector, a second detectorconnected with said intermediate frequency amplifier, a preselectorcircuit connected with the output of said second detector, an audiofrequency amplifier system connected with said preselector circuit and asource of audio frequency oscillation connected with said high frequencyoscillator, said preselector circuit being tuned to select the frequencyof said source of audio frequency oscillation.

. 2. A continuous wave radio telegraph receiving system comprising asuperheterodyne receiving circuit including-a first detector, a highfrequency oscillator connected therewith, an intermediate frequencyamplifier connected with said first detector, a second detectorconnected with said intermediate frequency amplifier, a preselectorcircuit comprising a tunable condenser and a winding of an audiofrequency transformer connected with the output of said second detector,an audio frequency amplifier system connected with said preselectorcircuit and a source oflaudio frequency oscillation connected'with' saidhigh frequency oscillator for continuously modulating the oscillationsimpressed on said first detector at an audio rate, the frequencyadjustment of said preselector circuit being matched to correspond tothe frequency of said source of audio frequency oscillations.

3. A- continuous wave radio telegraph receiving system comprising asuperheterodyne receiving circuit including a first detector, ahighfrequency oscillator connected therewith, an intermediate frequencyamplifier connected with said first detector, a second detectorconnected with said intermediate frequency amplifier, a preselectorcircuit connected with the output of said second detector, an audiofrequency am-- plifier system connected with said preselector circuit, asource of audio frequency oscillation connected between the grid andcathode of said high frequency oscillator for continuously modulatingthe oscillations-impressed on said first detector at an audio rate, anda radio' frequency by-pass condenser also connected to saidgrid andcathode, said preselector circuit being tuned to select the frequency ofsaid source of audio frequency oscillation.

4. A continuous wave radio telegraph receiving system comprising asuperheterodyne receiving circuit ,including- .afirst detector, 2. highfrequency oscillator connected therewith, an intermediate frequencyamplifier connected with said first'detector, a second detectorconnected with .said intermediate frequency amplifier, a preselectorcircuit comprising a variable condenser and an inductance connected withthe output of said second detector, an audio frequency amplifier systemconnected with said preselector cirouit.. a. source of plate supply forsaid high frequency oscillations, said source supplying energy for theplate circuits of said first and second detectors and said intermediateand audio frequency amplifiers, a source of audio frequency oscillationconnected between the grid and cathode of said high frequency oscillatorfor continuously modulating the oscillations impressed on said firstdetector at an audio rate, and means for bypassing the high frequencyoscillations generated by said oscillator around said source of audiofrequency oscillations, said condenser of said preselector circuit beingcapable of adjusting said circuit to the frequency of said audiofrequency source.

5. A continuous wave radio telegraph receiving system comprising asuperheterodyne receiving circuit including a first detector, a highfrequency oscillator having a tuned circuit connected at one end to thegrid of the oscillator, a connection between the other end of said tunedcircuit and the cathode, a transformer having the secondary windingthereof disposed in said connection, a source of audio frequencyoscillations connected with the primary winding of said transformer, anintermediate frequency amplifier connected with said first detector, asecond detector connected with said intermediate frequency amplifier, acommon source of plate supply for all stages of said receiving system, apreselector circuit connected with said second detector, and an audiofrequency amplification system connected with said preselector circuit,and means for adjusting said preselector circuit to the frequency ofsaid audio frequency source.

6. A continuous wave radio telegraph receiving system comprising asuperheterodyne receiving circuit including a first detector, a highfrequency oscillator having a tuned circuit connected at one end to thegrid of the oscillator, a connection between the other end of said tunedcircuit and the cathode, a transformer having the secondary windingthereof disposed in said connection, a source of audio frequencyoscillations connected with the primary winding of said transformer, anintermediate frequency amplifier connected with said first detector, asecond detector connected with said intermediate frequency amplifier, apreselector circuit connected with said second detector, an audiofrequency amplification system connected with said preselector circuit,means for adjusting said preselector circuit to the frequency of saidaudio frequency source, and means connected across the secondary windingof said transformer forming a closed path for the high frequencyoscillations generated by said oscillator around said source of audiofrequency oscillations.

7. A continuous wave radio telegraph receiving system comprising asuperheterodyne receiving circuit including a first detector, a highfrequency oscillator having a tuned circuit connected at one end to thegrid of the oscillator, a connection between the other end of said tunedcircuit and the cathode, a transformer having the secondary windingthereof disposed in said connection, a source of audio frequencyoscillations connected with the primary winding of said transformer, anintermediate frequency amplifier connected with said first detector, asecond detector connected with said intermediate frequency amplifier, apreselector circuit connected with said second detector, an audiofrequency amplification system connected with said 'preselector circuit,means for adjusting said preselector circuit to the frequency of saidaudio frequency source, and a condenser connected across the secondarywinding of said transformer for forming a closed path for the highfrequency oscillations generated by said oscillator around said sourceof audio frequency oscillations.

8. In a superheterodyne high-frequency signal receiving system, incombination, a first detector, a local oscillator coupled with the firstdetector for supplying an oscillation to beat with an incomingcontinuous wave signal to produce an intermediate frequency wave, anauxiliary os-' cillator adapted to modulate said local oscillator at aconstant audio frequency, said intermediate frequency wave being therebylikewise modulated and having besides the character of the incomingcontinuous wave signal, an intermediate frequency amplifier coupled withsaid first detector, a second detector, and an audio frequency amplifierpeaked at the said audio frequency.

9. In a superheterodyne high-frequency continuous wave signal receivingsystem, in combination, a first detector, a local oscillator, anintermediate frequency amplifier, a second detector, means formodulating the current in said intermediate frequency amplifier at aconstant audible frequency and in the character of the received signal,said audible frequency modulation being detected in said second detectorin the character of the received signal, and an audio frequency filterand a peaked audio frequency amplifier for selectively amplifying saidmodulation.

PERCIVAL D. LOWELL.

